The present invention relates to elemental analyzers and particularly an analyzer which employs a reagent assembly which is easily removable from the combustion chamber.
A determination of concentration of elements, such as carbon, hydrogen, sulfur, and nitrogen, in an organic sample is desirable for a variety of reasons. In recent years, the food market in particular has become interested in determining the amount of protein in an organic sample, which can be determined by the nitrogen content. Further, the sulfur content, as well as the carbon-to-hydrogen ratio, is desirable in the characterization of coal and coke samples, as are the carbon, hydrogen, and nitrogen ratios in a variety of other organic materials.
Elemental analyzers are commercially available from the Assignee of the present application, Leco Corporation of St. Joseph, Mich., which manufactures CHN analyzers, which are sold under the trademark TRUSPEC®. The analyzer may employ a variable volume ballast chamber of the type disclosed in U.S. Published Application 2004/0171165 A1 (now U.S. Pat. No. 7,070,738, the disclosure of which is incorporated herein by reference. The analyzer disclosed in this published application generally is used for the macro analysis of samples of from about 0.25 grams in size. The combustion system in such an analyzer uses a generally U-shaped quartz combustion tube of the type also disclosed in U.S. Pat. No. 4,622,009, the disclosure of which is incorporated herein by reference. The combustion tube includes a first vertically extending leg which receives a crucible for combustion of a sample and a second vertically extending leg downstream coupled to the first leg and which includes reagents that can serve several purposes. These include scrubbing undesirable products of combustion, enhancing the complete combustion of difficult samples, and/or the removal of excess reagents, such as oxygen. The selection of the reagent is dependent upon the characteristics of the application.
Generally, the analysis of elemental carbon, hydrogen, sulfur, and nitrogen is well known and is discussed in several references, including Methods in Microanalysis, Vol. 1, Mirra Osipovna Korshun, 1964, Instrumental Organic Elemental Analysis, R. Belcher, 1977; and Organic Elemental Analysis Ultramicro, Micro, and Trace Methods, Wolfgang J. Kirsten, 1983. U.S. Pat. No. 4,525,328 discloses an analyzer employing a fixed volume ballast chamber, which collects analytes in an approximately 4.5 L chamber for subsequent analysis. The amount of combustion oxygen used in filling the fixed ballast chamber is significant, and an analysis takes a significant amount of time for the combustion and ballast chamber filling. Also, the byproducts of combustion, i.e., the analyte gases, are somewhat diluted in the relatively large volume ballast chamber. The 2004/0171165 A1 application discloses a variable volume ballast chamber with a movable piston and a combustion detector, such that, during combustion of a sample, the chamber is only filled with byproducts of combustion until the completion of combustion is determined by the combustion detector. Typically, a significantly smaller volume than that of the fixed volume ballast chamber is captured in a more concentrated form of analyte which subsequently can be ejected from the variable volume ballast chamber by controlling a movable piston.
With the variable volume ballast chamber system disclosed in the above-identified published patent application, a large or macro analysis sized sample of 0.10 grams or more are employed. It is desired to provide an analyzer which utilizes a smaller samples, if possible, and conduct an analysis on-the-fly (i.e., detection of the sample during the combustion event as opposed to storing a combustion sample and providing an aliquot sample from a ballast chamber). One difficulty with an on-the-fly analysis system is that, for such micro analysis utilizing a helium carrier gas, an influx plug of excess oxygen is employed to fully combust the sample, and the remaining oxygen must be eliminated prior to detection by flowing the gaseous byproducts of combustion through a reduction reagent, such as copper wire strips.
In the U-shaped combustion tubes used in analyzers, such reagents are packed in the downstream leg of the U-shaped combustion tube and it is necessary after several analyses, which can be anywhere from less than 100 to about 1000 samples, to remove the fused and contaminated reduction reagent from the combustion tube and replace it with new reagents. This requires complete disassembly of the furnace and frequently replacement of the combustion tube itself inasmuch as the reagent packed in the quartz tube tends to melt and stick as a plug in the combustion tube itself. Since combustion takes place at a temperature of nearly 1000° C., this requires considerable time, expense, and manpower, since the furnace must first be cooled, opened, the combustion tube disassembled, and frequently a new combustion tube with a new reagent installed.
Thus, there exists a need for an improved system which allows for on-the-fly micro analysis, i.e. 2 mg to 10 mg samples, utilizing a combustion system which allows for the easy replacement of the reducing reagent.